Constantine IX Monomachos, reigned as Byzantine emperor from June 1042 to January 1055. He had been chosen by Empress Zoë Porphyrogenita as a husband and co-emperor in 1042, although he had been exiled for conspiring against her previous husband, Emperor Michael IV the Paphlagonian. They ruled together until Zoë died in 1050, and then ruled with Theodora Porphyrogenita until 1055.

During Constantine's reign, he led the Byzantine Empire in wars against groups which included the Kievan Rus', the Pechenegs and in the East against the rising Seljuq Turks. Constantine met these incursions with varying success, nonetheless, the empires borders remained largely intact since the conquests of Basil II, and Constantine would ultimately expand them eastwards, annexing the wealthy Armenian kingdom of Ani. As such he may be considered the last effective ruler of Byzantium’s apogee.

In the year before his death, in 1054, the Great Schism between the Eastern Orthodox and Roman Catholic Churches took place, culminating in Pope Leo IX excommunicating the Patriarch Michael Keroularios. Constantine was aware of the political and religious consequences of such a disunion, but his attempts to prevent it had been futile.